CHAPTER V
WATER CIRCULATION
Circulation of water in explosion-engines is one of the essentials of their perfect operation. Two special cases are encountered. In the one the jacket of the engine is supplied with running water; in the other, reservoirs are employed, the circulation being effected simply by the difference in specific gravity in a thermo-siphon apparatus. Coolers are also used.
Running Water.—A water-jacket fed from a constant source of running water, such as the water mains of a town, is certainly productive of the best results, the supply, moreover, being easily regulated; but the system is not widely used because the water runs away and is entirely lost. If running water be employed, the outlet of the jacket is so disposed that the water gushes out immediately on leaving the cylinder, and that the flow is visible and accessible, in order that the temperature may be tested by the hand. Apart from the relatively great cost of water in towns, the use of running water is objectionable on account of its chemical composition. Though it may be clear and limpid, it frequently contains lime salts, carbonates, sulphates, and silicates which are precipitated by reason of the sudden change of temperature to which the water is subjected as it
comes into contact with the walls of the cylinder. That part of the water-jacket surrounding the head or explosion-chamber, where the temperature is necessarily the highest, becomes literally covered with calcareous incrustations, which are the more harmful because they are bad conductors of heat and because they reduce and even obstruct the passage exactly at the point where the water must circulate most freely to do any good. If the circulating water be pumped into the jacket, it is preferable, wherever possible, to use cistern water, which is not likely to contain lime salts in suspension. If river water be used, it should be free from the objections already mentioned, which are all the more grave if the water be muddy, as sometimes happens. The water-jacket can be easily freed from all non-adhering deposits by flushing it periodically through the medium of a conveniently placed cock. It is always preferable to pass the water through a reservoir where its impurities can settle, before it flows to the cylinder. In the case considered, the water usually has an average temperature of 54 to 60 degrees F., under which condition the hourly flow should be at least 51⁄2 gallons per horse-power per hour, the temperature rising at the outlet-pipe of the cylinder to 140 and 158 degrees F., which should not be surpassed. However, in engines working with high compression, 104 to 122 degrees F. should not be exceeded.
If the water-jacket be fed by a reservoir, it is essential that the reservoir comply with the following conditions:
In horizontal engines the water-inlet is always located in the base of the cylinder, while the outlet is located at the top. By providing the inlet-pipe extending to the cylinder with a cock, the circulation of water can be regulated to correspond with the work performed by the engine. Another cock at the end of the outlet-pipe near the reservoir serves, in conjunction with the first, to arrest the circulating water. When the weather is very cold or when the cylinder must be repaired, these two cocks may be closed, and the pipe and water-jacket of the cylinder drained by means of the drain-cock V (Fig. 59), mounted at the inlet of the engine's water-jacket. In order that the pressure of the atmosphere may not prevent the flowing of the water, the highest part of the pipe is provided with a small tube, T, communicating with the atmosphere.
Fig. 59.—Thermo-siphon cooling system.